1. Introduction As the foundation of advanced manufacturing technologies (such as flexible manufacturing and computer-integrated manufacturing systems), CNC technology has received significant national investment in research and development. Major progress has been made in its key technologies, achieving multi-axis linkage and overcoming challenges in AC all-digital servo and spindle drive technologies. During the Ninth Five-Year Plan period, the goal of industrializing CNC machine tools was achieved, with domestically produced CNC machine tools accounting for 50% of the domestic market share, domestically produced CNC systems meeting 50% of the demand for state-owned CNC machine tools, and the CNC rate of output value exceeding 20%. Recent machine tool exhibitions show that many well-known international CNC system suppliers, such as Fanuc, Siemens, Yaskawa, and Mitsubishi, have launched mid-to-low-end CNC systems to cater to the rapidly developing Chinese market. Currently, economical CNC machine tool systems still dominate the domestic CNC system market. Most of these systems use MCS-51 series microcontrollers or microcontrollers compatible with the MCS-51 series, with a maximum clock frequency of 12-40MHz and a single-cycle instruction execution time of 250ns-1s. This limits the improvement of the performance of economical CNC machine tools, especially in functions such as multi-axis high-speed linkage, high-speed thread cutting, and high-resolution control. To achieve sub-micron level linear motion accuracy for the machine tool table, the introduction of modern control technology places higher demands on the processor. Refined control units, continuous feed with small program segments, and large data volumes, high-precision differential calculations and control also require the processor to respond to machining instructions at high speed, calculate the movement of the servo motor at high speed, and then issue control commands. Replacing the microcontroller with a high-performance digital signal processor (DSP) can improve the operating speed of the machine tool CNC system, enabling it to meet the requirements of high-speed and high-precision control. 2. CNC System Hardware Design 1. DSP Digital Signal Processor DSP digital signal processors have high clock frequencies and fast processing speeds, making them an ideal replacement for microcontrollers. The TI TMS320F240 digital signal processor (DSP) features an internal analog-to-digital converter (ADC) module including two independent sample-and-hold circuits and two 10-bit dual-slope converters, providing 16 analog input channels and the ability to convert two signals simultaneously. The DSP also increases the number and speed of serial and parallel ports, improving instruction processing time to tens of nanoseconds and achieving a data throughput of over 80 MIPS. This makes it ideal for high-speed data acquisition systems and real-time control systems with large data volumes, and it can perform FFT and wavelet analysis on the A/D conversion results. Therefore, DSPs are widely used in communications, remote sensing, speech and image processing, electronic measurement, automatic control, and pattern recognition. Typical application characteristics of DSPs include: a. Current DSPs employ a different architecture than general-purpose microprocessors (i.e., Harvard architecture), enabling pipelining. This allows instruction fetching, decoding, and execution to overlap, with instructions completed within a single machine cycle, significantly improving processing speed. b. High-speed computation: DSP chips have a dedicated hardware multiplier that can perform one multiplication and one addition within one instruction cycle, improving the efficiency of complex algorithms. c. Most new DSPs are equipped with a dedicated DMA bus and its controller, enabling parallel data transmission with little or no impact on DSP processing speed. This facilitates serial and parallel connections between DSPs, making it easier to implement a master-slave processor structure in CNC systems. The master processor handles front-end control (HMI management, information display, and preprocessor, etc.), while the slave processor handles back-end control, interpolation calculations, servo control, and feedback processing—frequent data operations and manipulations. d. To facilitate user design and debugging, many DSPs include on-chip JTAG emulation interfaces and high-level language compilers, allowing for simulation of program execution, interrupts, and timing, greatly enhancing convenience and making them ideal for CNC development. Therefore, DSPs have significant application value in high-performance CNC systems and have broad application prospects in precision servo control systems, tool detection and compensation and high-speed servo devices, and machine tool protection. 2. Main Control System Design The CNC system controls the lathe's main motion, feed motion, and auxiliary motion. Specifically, it controls keyboard input and output, the tool turret's travel in the X and Z directions, CNC tool turret indexing, switch closing, X and Z axis stepper motor phase detection, and spindle forward and reverse rotation. Its overall structure is shown in Figure 1. The TMS320f240 compares the current feedback position signal with the theoretical position calculated by interpolation using a specific interpolation algorithm. Through circumferential distribution, it determines the X and Z axis feed pulses. The feed pulses drive the X and Z axis stepper motors to complete the corresponding machining motions through opto-isolation and signal amplification. The software simultaneously handles speed control, tool turret indexing control, and thread machining programs. Precision CNC systems have extremely short interpolation cycles and small interpolation intervals, requiring frequent control and interpolation calculations. This necessitates the CNC system processing the position signals from each axis within a very short time (currently, the interpolation cycle has reached the millisecond level), making the adoption of the TMS320f240 processor essential. The TMS320f240 processor's powerful data processing capabilities and extremely high processing speed make it an excellent choice for precision CNC systems. It enables high-precision position servo control and contour machining control for precision machine tools, while also providing thermal and geometric error compensation and control for machine tools and cutting tools. General-purpose frequency converters use an AC-DC-AC configuration, first converting the mains frequency AC to DC via a rectifier, and then converting it back to AC with controllable frequency and voltage. The DSP controller, with its embedded PWM circuitry, A/D conversion circuitry, and other related circuits, can realize a fully digital control system for AC asynchronous motors. The TMS320f240 processor's embedded space vector state machine allows for easy switching of the six switching devices in the inverter bridge using space vector methods, ensuring the inverter bridge output voltage meets requirements. The spindle frequency conversion speed control system constructed using this processor improves voltage utilization and reduces harmonic effects compared to other PWM methods. 3. Large-capacity DSP program self-loading: After system power-on or reset, the TMS320f240's internal boot loader transfers the DSP program from the slow external E²PROM to the fast external SRAM for startup. However, this system requires more program memory than the 32K×8-bit limit. Therefore, specialized control logic must be designed to implement a secondary loading of the system program. The secondary loading bootloader and DSP runtime program are placed in the E²PROM. After power-on, the secondary loading bootloader is first loaded into the SRAM by the internal boot loader. Its task is to move the DSP runtime program from the EPROM to the SRAM and then transfer system control to the DSP runtime program. This method overcomes the limitation of the TE340f240 system's self-loading program capacity, allowing for the loading and execution of larger DSP programs. The DSP is equipped with 64K×16 SRAM, 64K×8 E²PROM, and 8K×8 DRAM. During the program loading phase after power-on or reset, the SRAM is mapped to the DSP's 64K×16 program memory space, and the E²PROM is mapped to the 64K×16 local data space and the 32K×16 global data space. The DSP is not allowed to operate on the DPRAM. During program execution, the SRAM corresponds to the 64K×16 program memory space and the local data memory space, and the DARAM corresponds to the global data memory space. The DSP is not allowed to operate on the E²PROM. Therefore, the chip select signal decoding of SRAM, DARAM, and E²PROM is as follows: CESRAM = ps × br × k × ds CEE²PROM = k + br + ds CEDARAM = k × br × ds Where ds is the data memory select pin, br is the bus request pin, ps is the program memory select pin; k is the mode conversion control bit. After power-on or reset, k = 0; after program execution, the DSP can make k = 1 through port operation to change the mapping range of each memory in the DSP memory space, realizing the redistribution of memory space range in SRAM, DARAM, and EPROM. 3 CNC System Software Design 1. Software Structure This economical CNC system realizes full software control and completes basic functions such as information processing, acceleration and deceleration control, appropriate change control, and servo control. It has point-to-point control function, continuous contour control function (linear interpolation, circular interpolation, and three-axis linkage function), tool radius and length compensation function, tool selection and exchange function, mirror machining function, fixed cycle function, etc. The system software structure is shown in Figure 2. a. The system offers multiple operation modes, including programming, parameter setting, automatic operation, idle operation, manual operation, zeroing (return to machine origin, return to program origin), MDI (automatic data input), communication, and teaching. Programming mode allows for inputting, retrieving, inserting, deleting, and copying part machining programs; automatic mode includes continuous and single-segment part machining, with real-time adjustment of the machining rate; idle operation mode simulates part machining, with continuous and single-segment operation options; manual mode adjusts the worktable position by pressing the direction keys, allowing for feed rate adjustment; zeroing mode manually returns the worktable to zero by pressing the direction keys; tool setting modes include manual and automatic tool setting (manual tool setting uses multiple trial cuts to determine the reference point, while automatic tool setting uses a dedicated tool setter for rapid reference point determination), with Chinese prompts for true human-machine interaction, making it simple and easy to learn; the teaching function meets the needs of current mechatronics teaching experiments. b. Comprehensive compensation functions. Examples include tool radius compensation, tool length compensation, and clearance compensation. In particular, it can achieve automatic transition functions for sharp corners and internal angles, effectively solving the machining problem of vertical cavities in mold processing. c. Multiple cyclic control functions effectively improve product processing efficiency and consistency. Examples include: linear equal division cycle, circular groove cycle, rectangular groove cycle, circular arc equal division cycle, contour cycle, deep hole drilling cycle, etc. In fact, the TMS320f240 digital signal processor has wide and effective applications in servo control, tool monitoring and compensation, fast servo operation, advanced control algorithms, and machine tool protection systems in precision CNC machining. 2. The application of improved control algorithms allows many advanced control strategies and methods, such as adaptive control, learning control, and friction control, to be applied to high-precision servo control systems, greatly improving control accuracy and speed. This system uses an improved time division method for interpolation calculations. Taking linear interpolation as an example: In coarse interpolation, the interpolation operation time is calculated based on the number of instructions used by the algorithm, as well as the feedback sampling period, accuracy, and speed, to determine the interpolation period T; the displacements DX and DZ of each coordinate in this interpolation period are calculated by combining the interpolation period T, the feed rate F, and the endpoint coordinates X and Z of the interpolated straight line segment; the actual feed amounts SX and SZ of each axis displacement in this interpolation period are calculated through feedback sampling and comparison, converted into the corresponding pulse number d'Z, and rounded to obtain dX and dZ; the DDA pulse allocation method is used to allocate the pulse number of the X and Z axes using the pulse allocation arrays dX(i) and dZ(j). In fine interpolation, the pulse arrays dXi(i) and dZ(i) allocated in coarse interpolation are sent to the pulse transmission interrupt service routine. This interrupt service routine is called by an interrupt generated by the programmable timer/counter inside the TM320f240. After responding to the interrupt, the pulse transmission interrupt service routine is invoked, and the corresponding content of the pulse array is checked. If the array content is 1, a pulse is sent to the hardware port; if it is 0, no pulse is sent. This completes the coordination and allocation of the feed pulses for each axis stepper motor within the current interpolation cycle. In actual operation, the system divides each interpolation cycle into 10 control cycles for servo control, thereby providing more effective control over the interpolation process and making the curve interpolation more accurate. The results show that this method greatly improves the accuracy and speed of the system's curve tracking. 4 Conclusion The high-speed performance of CNC machine tools based on DSP is greatly improved. The technical parameters achieved by the modified machine tool are: pulse equivalent, 0.005 mm/pulse in the X direction and 0.01 mm/pulse in the Z direction; maximum feed speed, 50 mm/s in the X direction and 100 mm/s in the Z direction; automatic feed speed, 1–100 mm/s; X and Z axis linkage; coordinate display resolution, 0.005 mm in the X direction and 0.01 mm in the Z direction. The application of DSP digital signal processors provides excellent tracking servo control for precision CNC servo control systems. After modifying the CNC system with a DSF processor, it can be used for closed-loop control of machine tools and control of other high-speed motion devices. Simultaneously, users can continuously upgrade the software and hardware at a low cost, always keeping pace with the development of CNC technology.